Jig for making contact with the electrodes of a dry contact rectifier



June 4, 1957 A. H. B. WALKER ETAL JIG FOR MAKING CONTACT WITH THEELECTRODES OF A DRY CONTACT RECTIFIER Filed Aug. 3, 1955 -r-i-Jl LEONARDALA/V (O/4t United States Patent M JIG FOR MAKING CONTACT WITH THE ELEC-TRODES OF A DRY CONTACT RECTIFIER Alec Hervey Bennett Walker and LeonardAlan Cole,

Kings Cross, London, England, assignors to Westinghouse Brake & SignalCompany Limited, London, England Application August 3, 1955, Serial No.526,169

Claims priority, application Great Britain September 13, 1954 7 Claims.(Cl. 219-19) This invention relates to a jig of the kind which issuitable for making contact with the electrodes of a dry contactrectifier element, the contact being made in such a manner that heavycurrent may be passed through the element without damaging it. 7

A jig of the kind described may be used in putting into effect themethod of manufacturing rectifier elements which is proposed in theco-pending application Serial No. 526,168, filed on August 3, 1955, byAlec Hervey Bennett Walker. ln the specification of that co-pendingapplication there is described a method of removing short circuits whichare formed during the process of punching the elements from a largesheet upon which the rectifying layer and counterelectrode havepreviously een formed, the short circuits occurring as a result of thecounterelectrode material being drawn across the edge of the elementthereby producing thin trails which bridge the gap between thecounterelectrode and the base plate at a number of places around thecircumference of the element. In the method proposed the short circuitsare removed, by applying a train of current pulses to the element in theforward direction such that the trails of counterelectrode material arevolatilised without damage to the element.

According to the invention, a jig of the kind described comprises afirst and a second metal block each having a contact surface, thecontact surfaces being parallel to each other, the blocks being movablein a direction perpendicular to the contact surfaces, the first blockbeing movable to a first or a second position and being subject to abiasing force which increases with the displacement of the block fromsaid first position, the second block being manually movable to a firstposition and to a second position in which, when a rectifier element ispositioned in the jig, the rectifier is gripped between the contactsurfaces and said first block is held in its second position, thedisplacement of said first block then being such that the biassing forcehas a predetermined value. I

Preferably the first metal block is spring biassed and the biassingforce is arranged to increase to the predetermined value by compressionof the spring as the second block is moved from its first to its secondposition. In this way the pressure exerted upon a rectifier elementpositioned between the contact blocks may be arranged to increasesteadily, thereby avoiding subjecting the rectifier element to a blowwhich might cause deformation when the contacts engage it.

Preferably also the contact surfaces of the blocks are of such a shapethat when they engage the opposite faces of an axially aligned rectifierelement the edges of the element project a short distance beyond theedges ofthe contact surfaces. These contact surfaces are convenientlyarranged to be horizontal.

The blocks may be arranged to have a mass which is large by comparisonwith that of the element in order Patented June 4, 1957 to reduce thetemperature rise of the element during the process of removing the shortcircuits.

If the rectifier element is placed with its counterelectrode adjacentthe first block the contact surface of the first block is preferablysmooth and faced with a highly conducting metal such as silver thecontact surface of the second block being roughened preferably byknurling, the second block being restrained from rotation and the firstblock being caused to rotate through a small angle about an axisperpendicular to the contact surfaces as the blocks move from theirfirst to their second positions. In this way the first contact block iscaused to rub on the counterelectrode and a good contact is therebyassured.

The jig is preferably interlocked with a switch which controls thecircuit supplying pulses of current, the interlock being such that nocurrent can flow until the force exerted upon the rectifier elementreaches a predetermined value that is, until the blocks aresubstantially in their second position.

One embodiment of the invention, suitable for treating circularrectifier elements, will now be described, by way of example, withreference to the accompanying drawing. As shown in the drawing, the jigcomprises two cylindrical brass blocks 1, 2 axially aligned one abovethe other and having their adjacent end faces 3, 4 horizontal andparallel to each other. The end face 3 is covered with a thin layer ofsilver and the end face 4 is knurled. The upper block 1 is fixed to thelower end of a rod 5 which is axially aligned with the blocks, the upperportion of the rod sliding longitudinally in an insulating bushing 6 andcarrying at its upper end a stop 7 which abuts against the upper end ofthe bushing 6 to limit the downward movement of the rod. A spring 8arranged coaxially with the rod 5 abuts at its upper end against thelower surface of the bushing 6 and at its lower end against the uppersurface of the upper contact block 1, the spring biassing the upperblock towards its first or'lower position. The lower block 2 is fixed tothe upper end of a second rod 9 which is coaxially aligned with thefirst rod 5 and which slides longitudinally in asecond insulatingbushing 10. The insulating bushings 6 and 10 are fixed to a support 11.The block 2 is biassed towards its first or lower position by means of aspring 12 which abuts at its upper end against the lower surface of thebushing 10 and at its lower end against a stop 13 which is fixed to therod 9. Downward movement of the block 2 is limited by the cam 14 uponwhich the lower end of the rod 9 rests. The cam 14 is fixed to a shaft15 and is manually rotatable through by means of the knob 16, the angleof rotation being limited by means of the stop 17 which is fixed to theknob 16 and the two stops 18 which are fixed to the support 11. Alsofixed to the shaft 15 is a second cam 19 which closes a limit switch 20when the block 2 is in its high position. The switch 20 controls theoperation of a supply circuit in such a manner that the circuit of thekind shown in Figure l is energised to supply pulses of current to theblocks only when the block 2 is in its high position; when the block 2is in its lower position the surfaces are separated from each other by anarrow gap.

The rod 5 is provided with a pin 22 which engages a cam slot 23 formedin the insulating bushing 6 and the rod 9 is provided with a pin 24which engages a cam slot 25 formed in the insulating bushing 10. The camslot 23 lies at an angle to the axis of the rods 5 and 9 The element,which is of a diameter slightly larger than that of the blocks 1, 2 isaxially aligned with the blocks and the knob 16 is then operated toraise thelower block 2. After the upper surface of the element hasabutted against the upper block further rotation of the knob 16 causescontinued upward movement of the blocks 1, 2 until the spring 8 issufficiently compressed toexert a force of four pounds weight on theupper block. As the blocks 1, 2 move upwards from their first or lowerpositions to their second or upper positions the pin 22 engaging the camslot 23 causes the block 1 to rotate through an angle of approximately20 and the pin 24 engaging the cam slot 25 prevents rotation of theblock 2. Engagement of the knurled surface 4 of the block 2 with thebase plate of the rectifier prevents rotation of the rectifier also. Asthe blocks move upwards, therefore, the surface 3 rubs against thecounter electrode and the force exerted by the surface 3 upon thecounterelectrode increases. In this way good electrical contact isassured. When the spring 8 is compressed to this degree the cam 19operates the limit switch 20 which energizes the supply circuit, thecircuit continuing to operate automatically in the manner indicatedabove to provide a train of ten pulses. At the end of the process theknob 16 is rotated to allow the rod 9 to move downwards, the switch 20is open and the element removed.

When the rectifier element has a central hole the contact blocks areprovided with central holes of slightly greater dimensions in order toallow the inner edge of the element to project inwards beyond theperimeter of the holes in the blocks. In this way the contact surfacesof the blocks are prevented from being contaminated by materialevaporated from the edges of the element.

The biassing force of four pounds weight has been found to besatisfactory for rectifier element sizes ranging from 1 to 4 squarecentimeters in area.

Having thus described our invention what we claim is:

1. A jig of the kind described comprising a first and a second metalblock by means of which contact is made to the two electrodes of arectifier element, the blocks being axially aligned and each having acontact surface, the contact surfaces being parallel to each other, theblocks being movable in a direction perpendicular to the contactsurfaces, the first blocks being movable to a first or a second positionand being subject to a biassing force tending to move it towards saidfirst position, said force increasing with the displacement of the blockfrom said first position, the second block being movable from a firstposition to a second position in which, when the rectifier element ispositioned in the jig, the element is gripped between the contactsurfaces and said first block is held in its second position, thedisplacement of said first block then being such that the biassing forcehas a predetermined value.

2. A jig of the kind described comprising a first and a second metalblock by means of which contact is made to the two electrodes of arectifier element, the blocks being axially aligned and each having acontact surface, the contact surfaces being parallel to each other, theblocks being movable in a direction perpendicular to the contactsurfaces, the first block movable to a first or a second position andbeing subject to a biassing force tending to move it towards said firstposition, said force increasing with the displacement of the block fromsaid first position, the second block being movable from a firstpositionto a second position in which, when the rectifier element ispositioned in the jig, the element is gripped between the contactsurfaces and said first block is held in its second position, thedisplacement of said first block then being such that the biassing forcehas a predetermined value, the contact surface of one block being smoothand faced with a highly conducting metal, the contact surface of theother block being roughened, and means for rotating saidone blockthrough a small angle about an axis perpendicular to the contactsurfaces as the blocks move from their first to their second position.

3. A jig of the kind described comprising a first and a second metalblock by means of which contact is made to the two electrodes of arectifier element, and an interlocking switch, the blocks being axiallyaligned and each having a contact surface, the contact surfaces beingparallel to each other, the blocks being movable in a directionperpendicular to the contact surfaces, the first block being movable toa first or a second position and being subject to a biassing forcetending to move it towards said first position, said force increasingwith the displacement of the block from said first position, the secondblock being movable from a first position to a second position in which,when the rectifier element is positioned in the jig, the element isgripped between the contact surfaces and said first block is held in itssecond position, the displacement of said first block then being suchthat the biassing force has a predetermined value, and means to operatesaid interlocking switch to cause current to be supplied to the jig whenthe blocks are substantially in their second position.

4. A jig of the kind described comprising a first and second block bymeans of which contact is made to the two electrodes of a rectifier, theblocks being axially aligned and each having an opposing surface forengaging the rectifier electrodes, one of said block surfaces beingsmooth and faced with a highly conducting metal, the other of said blocksurfaces being roughened, the blocks being movable in a directionperpendicular to the contact surfaces, said first block being movable toa first or a second position, biasing means tending to move said firstblock to its first position, said second block being movable to a firstor a second position, a second biasing means tending to move said secondblock to its first position, cam means for moving said second block toits second position, the rectifier being held between the contactsurfaces of said blocks, said second block moving said first blockagainst the biasing forces of both said resilient means to its secondposition, a second cam means associated with the one of said blocks forrotating said one block a limited degree as said one block is moved toits second position, and means for restraining rotation of the other ofsaid blocks as said other block is moved to its second position.

5. A jig of the kind described comprising a first and second block bymeans of which contact is made to the two electrodes of a rectifier, theblocks being axially aligned and each having an opposing surface forengaging the rectifier electrodes, one of said block surfaces beingsmooth and faced with a highly conducting metal, the other of said blocksurfaces being roughened, the blocks being movable in a directionperpendicular to the contact surfaces, said first block being movable toa first or a second position, biasing means tending to move said firstblock to its first position, said second block being movable to a firstor a second position, a second biasing means tending to move said secondblock to its first position, cam means for moving said second block toits second position, the rectifier being held between the contactsurfaces of said blocks, said second block moving said first blockagainst the biasing forces of both said resilient means to its secondposition, a first pin and slot connection associated with the one ofsaid blocks for rotating said one block a limited degree as said oneblock is moved to its second position, and a second pin and slotconnection for restraining rotation of the other of said blocks as saidother block is moved to its second position.

6. A jig of the kind described comprising a first and second block bymeans of which contact is made to the two electrodes of a rectifier, theblocks being axially aligned and each having an opposing surface forengaging the rectifier electrodes, one of said block surfaces beingsmooth and faced with a highly conducting metal, the other of said blocksurfaces being roughened, the blocks being movable in a directionperpendicular to the contact surfaces, said first block being movable toa first or a second position, biasing means tending to move said firstblock to its first position, said second block being movable to a firstor a second position, a second biasing means tending to move said secondblock to its first position, cam means for moving said second block toits second position, the rectifier being held between the contactsurfaces of said blocks, said second block moving said first blockagainst the biasing forces of both said resilient means to its secondposition, a second cam means associated with the one of said blocks forrotating said one block a limited degree as said one block is moved toits second position, means for restraining rotation of the other of saidblocks as said other block is moved to its second position, and a thirdcam means associated with said first cam means for actuating anelectrical switch when both said blocks are moved to their secondposition.

7. A jig of the kind described comprising a first and second block bymeans of which contact is made to the two electrodes of a rectifier, theblocks being axially aligned and each having an opposing surface forengaging the rectifier electrodes, one of said block surfaces beingsmooth and faced with a highly conducting metal, the other of said blocksurfaces being roughened, the blocks being movable in a directionperpendicular to the contact surfaces, said first block being movable toa first or a second position, biasing means tending to move said firstblock to its first position, said second block being movable to a firstor a second position, a second biasing means tending to move said secondblock to its first position, cam means for moving said second block toits second position, the rectifier being held between the contactsurfaces of said blocks, said second block moving said first blockagainst the biasing forces of both said resilient means to its secondposition, a first pin and slot connection associated with the one ofsaid blocks for rotating said one block a limited degree as said oneblock is moved to its second position, a second pin and slot connectionfor restraining rotation of the other of said blocks as said other blockis moved to its second position, and a second cam means associated withsaid first cam means for actuating an electrical switch when both saidblocks are moved to their second position.

References Cited in the file of this patent UNITED STATES PATENTS2,193,770 Piercy Mar. 12, 1940 2,253,702 Hall Aug. 26, 1941 2,457,691Kubic et a1 Dec. 28, 1948

